Vector Iterators Incompatible

Question

I have a class with a std::vector data member e.g.

class foo{
public:

const std::vector getVec(){return myVec;} //other stuff omitted

private:
s         


        

Answer 1

Another reason why this assert can trigger is if you would allocate "foo" with 'malloc' instead of 'new', effectively skipping the constructor(s).

It's unlikely to happen to a project developed from scratch in C++, but when converting plain-C code to C++ (replacing a static array[] in some struct with an stl-vector) you might just not realise that dynamic instances of said struct (and the members inside) are not going to have their constructor called - unless you also change 'malloc' to 'new'.

Answer 2

You are returning a copy of the vector. Because you are returning by value - your call to begin() and end() are for completely different vectors. You need to return a const & to it.

const std::vector<int> &getVec(){return myVec;}

I would do this slightly differently though. I'd make the class act a little like a standard container

class Data
{
   public:
      typedef std::vector<int>::const_iterator const_iterator;

      const_iterator begin() const { return myVec.begin(); }
      const_iterator end() const { return myVec.end(); }
};

Data::const_iterator i=myFoo.begin();

while(i != myFoo.end())
{
//
}

Answer 3

Change

const std::vector<int> getVec(){return myVec;}

to

const std::vector<int>& getVec(){return myVec;}

Answer 4

well, I don't think vector copy could be the only cause, that seems to be too obivious to me.

in my case I just find that corrupted stack, heap, uninteneded changes could also result in this failure, and it will in fact hiding the underlying reason. in my case, I changed to use indexer to iterate through and find the root cause.

Answer 5

Because you are returning by value - your call to begin() and end() are for completely different vectors. You need to return a const & to it

Answer 6

You are making a constant copy of the member vector, not accessing the member vector.

Change this:

const std::vector<int> getVec(){return myVec;} //other stuff omitted

to this:

const std::vector<int> & getVec(){return myVec;} //other stuff omitted

To go a little deeper, the iterator you get from this statement:

std::vector<int>::const_iterator i = myFoo.getVec().begin();

is an iterator to the temporary copy of your vector, which goes away after that statement executes, invalidating the iterator.